The present invention relates generally to mechanical compression release devices for internal combustion engines and, more particularly, to a device for providing compression relief to the valve located outboard on the camshaft relative to the cam gear.
Compression release mechanisms for internal combustion engines are well known in the art. Generally, these devices are provided to hold one of the valves in the combustion chamber of the cylinder head slightly open during the compression stroke while cranking the engine. This action partially relieves the force of compression in the cylinder during starting, so that starting torque requirements of the engine are greatly reduced. When the engine starts and reaches running speeds, the compression release mechanism is rendered inoperable so that the engine may achieve full performance. It is normally advantageous for the compression release mechanism to be associated with the exhaust valve so that the normal flow of the fuel/air mixture into the chamber through the intake valve, and the elimination of spent gases through the exhaust valve is not interrupted, and the normal direction of flow through the chamber is not reversed. Examples of such compression release mechanisms are disclosed in U.S. Pat. No. 4,977,868 issued to Holschuh and assigned to the assignee of the present invention, the disclosure of which is incorporated herein by reference.
Mechanically operated compression release mechanism disposed outboard of the outboard camshaft lobe which are operable to actuate an exhaust valve are also known in the art. The Holschuh patent discloses a centrifugally activated compression release mechanism having an auxiliary cam surface disposed at the outboard side of the outboard camshaft lobe. The auxiliary cam surface is rigidly attached to a pin which in turn is rotatably carried by an axially aligned bearing passage formed in each of the inboard and outboard lobes. The pin thus extends in a generally axial direction with respect to the camshaft. A flyweight is rigidly attached to the opposite end of the pin between the inboard camshaft lobe and the camshaft gear. A spring causes activation of a compression release valve in response to a stopped or slow engine speed; and centrifugal force imposed on the flyweight causes deactivation of a compression release valve in response to a higher engine speed.
U.S. Pat. No. 3,897,768 to issued to Thiel, also assigned to the assignee of the present invention, discloses a centrifugally activated compression relief mechanism fastened to the camshaft at the outboard side of the outboard camshaft lobe, and uses a plunger which extends through a bore formed in the camshaft.
Compression release mechanisms having a centrifugally activated movable member with slots formed therein for slidably engaging guide pins formed in or attached to conventional engine parts are also known. U.S. Pat. No. 4,651,687, issued to Yamashita, et al., for example, is directed to a compression release device for a four-cycle internal combustion engine. A movable member includes an elliptical and an L-shaped guide slot adapted to slidably engage a pair of pins fixed to the camshaft gear. Spring force causes the yoke to lift a tappet during the compression cycle when starting the engine; and centrifugal force causes the yoke to lie coincident with the camshaft lobe surface when normal engine operation speed is attained. One disadvantage of this apparatus is that it requires a rather complicated guiding arrangement for movement of the yoke In addition, the apparatus requires that the camshaft gear be physically altered and operates to lift only the inboard valve disposed adjacent the camshaft gear.